Field of the Disclosure
The disclosure relates in general to a multi-stage discharge circuit for an electronic device and a multi-stage discharge method for the same.
Description of the Related Art
The electronic device may employ a high-voltage element (such as a motor and a relay). To assure smooth operation, the electronic device normally stabilizes the voltage with a large capacitor coupled to a system power. However, when the electronic device is turned off, problems such as system malfunction, system crash and electric shock may occur if the charges stored in the large capacitor are not fully and quickly discharged.
Therefore, many discharge technologies are provided to resolve the above problems. FIG. 1 and FIG. 2 show two discharge circuits.
FIG. 1 is a schematic diagram of a resident resistive type discharge circuit. As indicated in FIG. 1, the discharge circuit includes a capacitor C and a discharge resistor R which are connected in parallel. The capacitor R normally has a large resistance and is capable of bearing a large current during the discharge process. After a system power VDD is turned off, the capacitor C and the resistor R form a discharge path P1, and the charges stored in the capacitor C may be discharged through the resistor R. However, FIG. 1 is disadvantaged in that the discharge speed is not fast enough and the resistor R keeps consuming power during the normal operation of the system.
FIG. 2 is a schematic diagram of a freewheeling diode discharge circuit. As indicated in FIG. 2, the discharge circuit includes a freewheeling diode D. When the system power VDD is turned on, the freewheeling diode D is backward-biased and is not conducted. When the system power VDD is turned off, the charges of the capacitor C cause the freewheeling diode D to be forward-biased and thus conducted. Therefore, the capacitor C and the freewheeling diode D form a discharge path P2, and the charges stored in the capacitor C may be discharged through the freewheeling diode D. However, FIG. 2 is disadvantaged in that the discharge speed is not fast enough.